1. Field of the Invention
This invention relates to polymeric adhesive compositions and their use in radiation-sensitive elements and particularly photographic elements and processes to obtain a desirable combination of properties. In particular, this invention relates to heat-activatable, amorphous, organic solvent-soluble adhesive compositions capable of binding hydrophilic surfaces to hydrophobic surfaces in photographic materials. A preferred embodiment of this invention is the use of these adhesive compositions in photographic film units.
2. Description of the Prior Art
It is well-known that certain condensation polymers are useful as adhesives. For instance, U.S. Pat. No. 3,694,212 of Richter et al issued Sept. 26, 1972, discloses an adhesive for photographic materials comprising a reaction product of glycerin with an aliphatic dicarboxylic acid. U.S. Pat. No. 3,313,676 of Kamal et al issued Apr. 11, 1967, relates to laminate crosslinkable adhesives having unsaturated dicarboxylic acid moieties. U.S. Pat. No. 3,629,360 of Burkhart et al issued Dec. 21, 1971, relates to phenol-modified coumarone-indene resins blended with copolyesters in an adhesive mixture. German Patent No. 1568-342 (Chemical Abstract 53885 V.30) relates to adhesives made from polyesters containing carbonate groups. U.S. Pat. No. 3,013,914 of Willard issued Dec. 19, 1961, discloses polyesters made from at least two diacids and two diols which are useful as hot melt adhesives for metal-can seams. Adhesives for splicing motion-picture film are disclosed in U.S. Pat. No. 3,117,901 of Chamber issued Jan. 14, 1964. Polyester adhesives for leather goods are described in U.S. Pat. Nos. 3,136,677 of Woker issued June 9, 1964, and 3,505,293 of Bond et al issued Apr. 7, 1970. U.S. Pat. No. 3,652,502 of Jackson et al issued Mar. 28, 1972, relates to crystalline polyester adhesives which have free carboxyl groups useful in metal and electrical products. U.S. Pat. No. 1,852,375 of Biethau et al issued Dec. 3, 1924, relates to polyesters plasticized with aminoplasts useful in varnishes and enamels.
It is also well-known to use polyester adhesives in laminates, as disclosed in U.S. Pat. No. 3,054,703 of Brasure issued Sept. 18, 1962. These adhesives are polyesters of a terephthalic acid with a branched alkyl glycol to bond polyethylene terephthalate to various materials. This reference, however, fails to teach or suggest the use of a polyester adhesive which has a glycol component comprising any di-, tri- or tetraethylene glycol or 1,4-bis(2-hydroxyethoxy)cyclohexane. An adhesive made with only a branched aliphatic glycol and without a linear aliphatic glycol has undesirably low bonding strengths. U.S. Pat. No. 3,372,148 of Wiener issued Mar. 5, 1963, describes amorphous polyester adhesives made from ethylene glycol, dimethyl hexahydroterephthalate and dimethyl terephthalate used in fibrous sheet materials. These adhesives crystallize upon application of heat.
U.S. Pat. No. 3,515,628 of Jackson et al issued June 2, 1970, relates to hot melt adhesives for metal-can seams and resins having a glass transition temperature below 30.degree. C. and a crystallinity within the range of 5 to 25%. These polyesters are made from a phthalic acid and any alkylene glycol. The reference teaches that most polyesters with less than 5% crystallinity have undesirably low adhesive strengths at temperatures above 50.degree. C. The polyesters described in this patent, however, have not been found to be useful in the formation of photographic film units as they exhibit low peel strength at higher temperatures.
U.S. Pat. No. 3,036,913 of Burg issued May 29, 1962, relates to the use of polyester subbing layers to bond photopolymerizable layers to supports in photopolymerizable elements. These adhesives comprise thermally sensitive addition polymerization catalysts which are light-activated.
In U.S. Pat. No. 3,658,541 of Jacoby et al issued Apr. 25, 1972, are described polyester adhesive subbing layers having an adhesive comprising ethylene glycol as the glycol component, which is used to render gelatinous compositions adherent to polyester supports in photographic elements. The polyesters are modified with an acid modifying agent and an organic dianhydride to render them soluble in organic solvents such as methylene chloride.
Various formats for photographic film units are described in U.S. Pat. Nos. 2,352,014 of Rott issued June 20, 1944, 2,543,181 of Land issued Feb. 27, 1951, 2,983,606 of Rogers issued May 9, 1961, 3,020,155 of Yackel et al issued Feb. 6, 1962, 3,227,550 of Whitmore et al issued Jan. 4, 1966, 3,227,552 of Whitmore issued Jan. 4, 1966, 3,415,644, 3,415,645 and 3,415,646, all of Land and issued Dec. 10, 1968, 3,635,707 of Cole issued Jan. 18, 1972, 3,362,819 and 3,362,821, both of Land and issued Jan. 9, 1968, 3,647,437 of Land issued Mar. 7, 1972, and 3,756,815 of Schlein et al issued Sept. 4, 1973, Canadian Pat. Nos. 674,082 of Whitmore issued Nov. 12, 1963, and 928,559 of Cole issued June 19, 1973, Belgian Pat. Nos. 757,959 and 757,960, British Pat. Nos. 904,364 and 840,731, and copending U.S. application Ser. No. 676,945 of Hannie filed Apr. 14, 1976. None of these references teaches or suggests the adhesive compositions disclosed herein or their use in photographic materials.
In these formats, the image-receiving layer containing the photographic image for viewing can be separated from the photographic layers after processing or, in some embodiments, it can remain permanently attached and integral with the image-generating and ancillary layers present in the structure when a transparent support is employed on the viewing side of the assemblage. The image is formed by color-providing substances released from the image-generating units, diffusing through the layers of the structure to the dye image-receiving layer. After exposure of the assemblage, an alkaline processing composition permeates the various layers to initiate development of the exposed photosensitive silver halide emulsion layers. The emulsion layers are developed in proportion to the extent of the respective exposures, and the color-providing materials which are formed or released in the respective image-generating layers begin to diffuse throughout the structure. At least a portion of the imagewise-distributed or released color-providing substances migrates to the dye image-receiving layer to form an image of the original subject.
Typically, adhesives are used in photographic film units to bond supports, subbed or unsubbed, to cover sheets or other layers around the edges of the units. Adhesives can also be used to bond subbing layers to supports or cover sheets, photosensitive layers to image-receiving layers, and the like. It has been also desirable to provide high-strength adhesives for bonding spacer rail substrates to other layers, such as barrier timing layers, supports, photosensitive layers and the like. These spacer rail substrates generally separate the photosensitive element of the film unit from a cover sheet which contains the barrier timing layer. However, due to many prerequisites for acceptable bonding at low and moderate temperatures of spacer rail substrates to other layers, none of the prior-art adhesives is useful in these photographic materials.
Most polyester adhesives taught in the art exhibit extremely low bonding strengths at moderate to high temperatures, such as within the range of 40.degree. C. to 90.degree. C. Hence, they must be used at low temperatures, undesirably limiting manufacturing and processing conditions. Further these prior-art adhesives do not satisfactorily bond all types of materials. For instance, some can be used only to bond hydrophilic surfaces, and others adhere only to hydrophobic surfaces. Still further, most adhesives known in the art are crystalline in nature or are not conducive to heat-sealing or dielectric sealing techniques.
It is evident, then, that there is a need in the photographic arts for amorphous adhesives which are heat-activatable and which have high bonding strengths over a wide range of temperatures.